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Photos of Dolomedes tenebrosus by Matt Welter, curator at the Neville Public Museum of Brown County

Dolomedes close-up/M. Welter.

Close-up of Dolomedes tenebrosus showing its two rows of eyes.

The next time you go fishing or visit your summer cabin at the lake look for fishing spiders. The spider Dolomedes tenebrosus shown above is the largest spider in northeast WI. All spiders in the genus Dolomedes can hunt using "water as a web". They position themselves with their back legs resting on shoreline debris or vegetation and their front legs stretched out over the surface of the water. Their legs are covered with hairs and spines (see above photo) that allow them to feel vibrations in the water's sutrface tension. If they sense a prey item like an insect, tadpoles, or small fish, they can skate over the water surface and reach down to capture their prey. They can also crawl along vegetation underwater to stalk and capture prey. D. tenebrosus is often found far from water, and will hunt terrestrial insects, like crickets, as well.

Dolomedes species belong to a family of spiders (Pisauridae) commonly called "nursery web spiders", but because of their large size, they are sometimes mistaken for Wolf spiders (Family: Lycosidae). While spiders in these two families are very similar in their basic shape (morphology), and reproductive behavior, in that they both carry around their egg sacs and care for their young, they have several important differences. Pisaurids carry their egg sacs in their chelicerae (jaws) and attached to their spinnerets, and make a "nursery web" in vegetation that the young are born in. Wolf spider females carry their egg sacs behind them attached to their spinnerets and carry their spiderlings on their backs after they are born. And of course, wolf spiders do not fish.

Fishing spiders are also sometimes confused with Argyroneta aquatica, or "Water Spider" of the Paleoarctic (Europe and northern Asia, together with Africa north of the Sahara). Argyroneta aquatica is the only spider that lives primarily under the water by creating a diving bell by filling an underwater silk retreat with air that it traps at the surface on its hairy abdomen.

There are six species of fishing spiders found in the Great Lakes states. Look for them in swampy areas, near ponds and lakes in vegetation, on docks and pilings, on bridges, tree trunks, rocks and logs. Some species roam farther away from water and can be found in dry woods, wood piles, and sometimes in cabins or houses. You can find which Dolomedes, Pisaurids, Lycosids, or other spiders occur in your state searching the database The Spider Species of the Great Lakes States.

More information about Dolomedes

 


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Last updated on April 15, 2014